The proposed research is a continuation of our ongoing randomized, double- blind skin cancer prevention trial initiated in 1985. The objective of the project is to complete the cancer prevention trial to compare the effectiveness of 13-cis retinoic acid (13-cRA) versus retinol (ROH) versus placebo in the prevention of basal cell cancer (BCC) and cutaneous squamous cell cancer (SCC) in subjects with a prior history of at least four of these lesions. The hypotheses to be evaluated include: 1) A supplement of 5-10 mg per day of 13-cRA will reduce the incidence of new BCC/SCC when compared to placebo. 2) A supplement of 25,000 IU retinol will reduce the incidence of new BCC/SCC when compared to placebo. The specific aims of this trial include: 1) To randomize at least 498 eligible subjects to 13-cRA, ROH, or placebo. 2) To motivate and determine the frequency and degree of protocol compliance. 3) To determine the frequency, type, and degree of adverse or protective health events. 4) To compare the number, incidence rate, and the time to diagnosis of new skin cancers. 5) To determine plasma concentrations of ROH and retinyl palmitate for each subject's initial accrual visit and for selected subjects at their follow- up visits. 6) To collect and freeze plasma samples from subjects for future analyses of other nutrients. 7) To determine the effects of ROH and 13-cRA as immunomodulators or key cellular immune functions.